I need to buy a new computer I am looking at a Lenovo all in one 23.8 ultra HD 4k display with a i5 processor or an imac the specs are nearly the same but I can save about 700$ with the Lenovo. Which one will run Lightroom 4 and photoshop best? I have read about some trouble with imac's and Lightroom.
I would not even try running Lightroom 4 with a 4K display, it will probably be so slow that you can't use it. If you're going to spend the money to buy a new computer, you probably also want to spend 79 US dollars to upgrade to Lightroom 6, or $9.99 for Lightroom CC, these at least have the potential of running well on a 4K display. You will also need a powerful graphics card.
More details are here: